Inverter switching frequency control systems and methods

ABSTRACT

A motor control system includes: a voltage command module configured to determine a target d-axis voltage for an electric motor and a target q-axis voltage for the electric motor; a target frequency module configured to: selectively set a target switching frequency to a first predetermined switching frequency; and selectively set the target switching frequency to a second predetermined switching frequency that is at least 2 kilohertz (kHz) greater than the first predetermined switching frequency; and a switching module configured to: based on the target d-axis voltage and the target q-axis voltage, determine target pulse width modulation (PWM) duty cycles for phases, respectively, of the electric motor; and switch switches of legs of an inverter module connected to the phases of the electric motor at the target PWM duty cycles, respectively, and the target switching frequency.

INTRODUCTION

The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

The present disclosure relates to inverters for motors of vehicles and more particularly to systems and methods for controlling switching of inverters.

Some types of vehicles include only an internal combustion engine that generates propulsion torque. Electric vehicles may not include an internal combustion engine and may rely on one or more electric motors for propulsion.

Hybrid vehicles include both an internal combustion engine and one or more electric motors. Some types of hybrid vehicles utilize the electric motor and the internal combustion engine in an effort to achieve greater fuel efficiency than if only the internal combustion engine was used. Some types of hybrid vehicles utilize the electric motor and the internal combustion engine to achieve greater torque output than the internal combustion could achieve by itself.

Some example types of hybrid vehicles include parallel hybrid vehicles, series hybrid vehicles, and other types of hybrid vehicles. In a parallel hybrid vehicle, the electric motor works in parallel with the engine to combine power and range advantages of the engine with efficiency and regenerative braking advantages of electric motors. In a series hybrid vehicle, the engine drives a generator to produce electricity for the electric motor, and the electric motor drives a transmission. This allows the electric motor to assume some of the power responsibilities of the engine, which may permit the use of a smaller and possibly more efficient engine.

SUMMARY

In a feature, a motor control system includes: a voltage command module configured to determine a target d-axis voltage for an electric motor and a target q-axis voltage for the electric motor; a target frequency module configured to: selectively set a target switching frequency to a first predetermined switching frequency; and selectively set the target switching frequency to a second predetermined switching frequency that is at least 2 kilohertz (kHz) greater than the first predetermined switching frequency; and a switching module configured to: based on the target d-axis voltage and the target q-axis voltage, determine target pulse width modulation (PWM) duty cycles for phases, respectively, of the electric motor; and switch switches of legs of an inverter module connected to the phases of the electric motor at the target PWM duty cycles, respectively, and the target switching frequency.

In further features, the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a torque of the electric motor and a speed of the electric motor.

In further features, the target frequency module is configured to: based on the torque and the speed, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency within the fundamental electrical period of sinusoidal phase current; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.

In further features, the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a d-axis current of the electric motor.

In further features, the target frequency module is configured to: based on the d-axis current of the electric motor, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.

In further features, the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a q-axis current of the electric motor.

In further features, the target frequency module is configured to: based on the q-axis current of the electric motor, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.

In further features, the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on at least one current of at least one of the phases of the electric motor.

In further features, the target frequency module is configured to: based on the at least one current of the at least one of the phases, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.

In further features, the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a stator current that is equal to a square root of a sum of (a) a d-axis current of the electric motor squared and (b) a q-axis current of the electric motor squared.

In further features, the target frequency module is configured to: based on the stator current, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.

In further features, the first predetermined switching frequency is 10 kHz.

In further features, the second predetermined switching frequency is approximately 15 kHz.

In further features, the second predetermined switching frequency is approximately 20 kHz.

In further features, the voltage command module is configured to determine the target d-axis voltage for the electric motor and the target q-axis voltage for the electric motor based on minimizing: a first error between a d-axis current of the electric motor and a target d-axis current of the electric motor; and a second error between a q-axis current of the electric motor and a target q-axis current of the electric motor.

In further features, a current command module is configured to set the target d-axis current and the target q-axis current based on a torque request for the electric motor.

In further features, the target frequency module is configured to selectively set the target switching frequency to the second predetermined switching frequency for 6 different periods during the period of a fundamental electrical period of sinusoidal phase current.

In a feature, a motor control method includes: determining a target d-axis voltage for an electric motor and a target q-axis voltage for the electric motor; selectively setting a target switching frequency to a first predetermined switching frequency; selectively setting the target switching frequency to a second predetermined switching frequency that is at least 2 kilohertz (kHz) greater than the first predetermined switching frequency; based on the target d-axis voltage and the target q-axis voltage, determining target pulse width modulation (PWM) duty cycles for phases, respectively, of the electric motor; and switching switches of legs of an inverter module connected to the phases of the electric motor at the target PWM duty cycles, respectively, and the target switching frequency.

In further features, the motor control method further includes determining whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a torque of the electric motor and a speed of the electric motor.

In further features, the motor control method further includes: based on the torque and the speed, setting a starting time and a period for setting the target switching frequency to the second predetermined switching frequency within the fundamental electrical period of sinusoidal phase current; and setting the target switching frequency to the second predetermined switching frequency at the starting time for the period.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example vehicle system;

FIG. 2 is a functional block diagram of an example propulsion control system;

FIG. 3 includes a schematic including an example implementation of a power control system;

FIG. 4 includes a schematic of an example implementation of an inverter module;

FIG. 5 includes a functional block diagram of an example motor control module;

FIG. 6 includes example graphs of pulse width modulation (PWM) duty cycles over time;

FIG. 7 is a flowchart depicting an example method of setting a target switching frequency for an inverter module and controlling switching of the inverter module at the target switching frequency; and

FIG. 8 includes an example graph of currents and a ripple tracking pulse over time.

In the drawings, reference numbers may be reused to identify similar and/or identical elements.

DETAILED DESCRIPTION

An inverter module of a vehicle includes legs of switches that regulate current flow (a) from a battery to an electric motor and (b) from the electric motor to the battery. A direct current (DC) bus capacitor may be connected between the inverter module and the battery. Pulse width modulated (PWM) signals are used to control switching of the legs. A fixed predetermined switching frequency for the PWM signals could be used, such as 10 kiloHertz (kHz) for automotive applications.

According to the present application, a control module uses the predetermined switching frequency under some circumstances but uses a second (higher) predetermined switching frequency under other circumstances, such as where alternating current (AC) current ripple of the inverter output/input to the motor would be higher. The use of the second predetermined switching frequency decreases losses of the system, reduces AC current ripple, and total harmonic distortion (THD), decreases noise, vibration, and harshness (NVH) of the motor, and decreases probability of resonances. The second predetermined switching frequency may be, for example, 2 times the predetermined switching frequency (e.g., 20 kHz).

Referring now to FIG. 1 , a functional block diagram of an example vehicle system is presented. While a vehicle system for a hybrid vehicle is shown and will be described, the present disclosure is also applicable to electric vehicles that do not include an internal combustion engine (including pure electric vehicles), fuel cell vehicles, autonomous vehicles, semi-autonomous vehicles, non-autonomous vehicles, and other types of vehicles. Also, while the example of a vehicle is provided, the present application is also applicable to non-vehicle implementations.

An engine 102 may combust an air/fuel mixture to generate drive torque. An engine control module (ECM) 114 controls the engine 102. For example, the ECM 114 may control actuation of engine actuators, such as a throttle valve, one or more spark plugs, one or more fuel injectors, valve actuators, camshaft phasers, an exhaust gas recirculation (EGR) valve, one or more boost devices, and other suitable engine actuators. In some types of vehicles (e.g., electric vehicles), the engine 102 may be omitted.

The engine 102 may output torque to a transmission 195. A transmission control module (TCM) 194 controls operation of the transmission 195. For example, the TCM 194 may control gear selection within the transmission 195 and one or more torque transfer devices (e.g., a torque converter, one or more clutches, etc.).

The vehicle system includes one or more electric motors, such as electric motor 198. An electric motor can act as either a generator or as a motor at a given time. When acting as a generator, an electric motor converts mechanical energy into electrical energy. The electrical energy can be, for example, used to charge a battery 199. When acting as a motor, an electric motor generates torque that may be used, for example, for vehicle propulsion. While the example of one electric motor is provided, the vehicle may include more than one electric motor.

A motor control module 196 controls power flow from the battery 199 to the electric motor 198 and from the electric motor 198 to the battery 199. The motor control module 196 applies electrical power from the battery 199 to the electric motor 198 to cause the electric motor 198 to output positive torque, such as for vehicle propulsion. The battery 199 may include, for example, one or more batteries and/or battery packs.

The electric motor 198 may output torque, for example, to an input shaft of the transmission 195 or to an output shaft of the transmission 195. A clutch 200 may be engaged to couple the electric motor 198 to the transmission 195 and disengaged to decouple the electric motor 198 from the transmission 195. One or more gearing devices may be implemented between an output of the clutch 200 and an input of the transmission 195 to provide a predetermined ratio between rotation of the electric motor 198 and rotation of the input of the transmission 195.

The motor control module 196 may also selectively convert mechanical energy of the vehicle into electrical energy. More specifically, the electric motor 198 generates and outputs power via back EMF when the electric motor 198 is being driven by the transmission 195 and the motor control module 196 is not applying power to the electric motor 198 from the battery 199. The motor control module 196 may charge the battery 199 via the power output by the electric motor 198.

Referring now to FIG. 2 , a functional block diagram of an example propulsion control system is presented. A driver torque module 204 determines a driver torque request 208 based on driver input 212. The driver input 212 may include, for example, an accelerator pedal position (APP), a brake pedal position (BPP), cruise control input, and/or an autonomous input. In various implementations, the cruise control input may be provided by an adaptive cruise control system that attempts to maintain at least a predetermined distance between the vehicle and objects in a path of the vehicle. The autonomous input may be provided by an autonomous driving system that controls movement of a vehicle from location to location while avoiding objects and other vehicles. The driver torque module 204 may determine the driver torque request 208 using one or more lookup tables or equations that relate the driver inputs to driver torque requests. The APP and BPP may be measured using one or more APP sensors and BPP sensors, respectively.

The driver torque request 208 may be an axle torque request. Axle torques (including axle torque requests) refer to torque at the wheels. As discussed further below, propulsion torques (including propulsion torque requests) are different than axle torques in that propulsion torques may refer to torque at a transmission input shaft.

An axle torque arbitration module 216 arbitrates between the driver torque request 208 and other axle torque requests 220. Axle torque (torque at the wheels) may be produced by various sources including the engine 102 and/or one or more electric motors, such as the electric motor 198. Examples of the other axle torque requests 220 include, but are not limited to, a torque reduction requested by a traction control system when positive wheel slip is detected, a torque increase request to counteract negative wheel slip, brake management requests to reduce axle torque to ensure that the axle torque does not exceed the ability of the brakes to hold the vehicle when the vehicle is stopped, and vehicle over-speed torque requests to reduce the axle torque to prevent the vehicle from exceeding a predetermined speed. The axle torque arbitration module 216 outputs one or more axle torque requests 224 based on the results of arbitrating between the received axle torque requests 208 and 220.

In hybrid vehicles, a hybrid module 228 may determine how much of the one or more axle torque requests 224 should be produced by the engine 102 and how much of the one or more axle torque requests 224 should be produced by the electric motor 198. The example of the electric motor 198 will be continued for simplicity, but multiple electric motors may be used. The hybrid module 228 outputs one or more engine torque requests 232 to a propulsion torque arbitration module 236. The engine torque requests 232 indicate a requested torque output of the engine 102.

The hybrid module 228 also outputs a motor torque request 234 to the motor control module 196. The motor torque request 234 indicates a requested torque output (positive or negative) of the electric motor 198. In vehicles where the engine 102 is omitted (e.g., electric vehicles) or is not connected to output propulsion torque for the vehicle, the axle torque arbitration module 216 may output one axle torque request and the motor torque request 234 may be equal to that axle torque request.

In the example of an electric vehicle, the ECM 114 may be omitted, and the driver torque module 204 and the axle torque arbitration module 216 may be implemented within the motor control module 196. In electric vehicles, the driver torque module 204 may input the driver torque request 208 to the motor control module 196, and the components related to controlling engine actuators may be omitted.

The propulsion torque arbitration module 236 converts the engine torque requests 232 from an axle torque domain (torque at the wheels) into a propulsion torque domain (e.g., torque at an input shaft of the transmission). The propulsion torque arbitration module 236 arbitrates the converted torque requests with other propulsion torque requests 240. Examples of the other propulsion torque requests 240 include, but are not limited to, torque reductions requested for engine over-speed protection and torque increases requested for stall prevention. The propulsion torque arbitration module 236 may output one or more propulsion torque requests 244 as a result of the arbitration.

An actuator control module 248 controls actuators 252 of the engine 102 based on the propulsion torque requests 244. For example, based on the propulsion torque requests 244, the actuator control module 248 may control opening of a throttle valve, timing of spark provided by spark plugs, timing and amount of fuel injected by fuel injectors, cylinder actuation/deactivation, intake and exhaust valve phasing, output of one or more boost devices (e.g., turbochargers, superchargers, etc.), opening of an EGR valve, and/or one or more other engine actuators. In various implementations, the propulsion torque requests 244 may be adjusted or modified before use by the actuator control module 248, such as to create a torque reserve.

The motor control module 196 controls switching of switches of an inverter module based on the motor torque request 234, as discussed further below. The inverter module converts direct current (DC) power into alternating current (AC) power. The inverter module applies AC power to motor 198. Switching of the inverter module controls torque of the electric motor 198. The inverter module also converts power generated by the electric motor 198 into DC power and outputs DC power for the battery 199, for example, to charge the battery 199.

The inverter module includes a plurality of switches, such as three legs of switches. The motor control module switches the switches to apply alternating current (AC) power to the electric motor 198 to drive the electric motor 198. For example, the inverter module may generate n-phase AC power and apply the n-phase AC power to (e.g., a, b, and c, or u, v, and w) n stator windings of the electric motor 198. In various implementations, n is equal to 3. Magnetic flux produced via current flow through the stator windings drives a rotor of the electric motor 198. The rotor is connected to and drives rotation of an output shaft of the electric motor 198. The output shaft of the electric motor 198 is connected to one or more wheels of the vehicle.

In various implementations, one or more filters (e.g. capacitors) may be electrically connected between the inverter module and the battery 199. The one or more filters may be implemented, for example, to filter power flow to and from the battery 199. As an example, a filter including one or more capacitors and resistors may be electrically connected in parallel with the battery 199 and the inverter module.

FIG. 3 includes a schematic including an example implementation of a power control system. The battery 199 may also be referred to or include a battery pack, as discussed above.

High (positive, DC+) and low (negative, DC−) sides 304 and 308 are connected to positive and negative terminals, respectively, of the battery 199. One or more capacitors, such as capacitor 312, are connected in parallel with the battery 199 between the high and low sides 304 and 308. The capacitor(s) stabilize the DC bus and provide a low impedance voltage source to the inverter module since the battery 199 may have a higher impedance.

An inverter module 316 includes three legs, one leg connected to each phase of the electric motor 198. The inverter module 316 controls current flow to the legs/phases of the electric motor 198. The inverter module 316 converts DC power from the high and low sides 304 and 308 into 3-phase AC power and outputs the AC power to the electric motor 198.

FIG. 4 includes a schematic of an example implementation of the inverter module 316. The inverter module 316 includes three legs. One leg is connected to each phase of the electric motor 198.

A first leg 512 includes first and second switches 516 and 520. The switches 516 and 520 each include a first terminal, a second terminal, and a control terminal. Each of the switches 516 and 520 may be an insulated gate bipolar transistor (IGBT), a field effect transistor (FET), such as a metal oxide semiconductor FET (MOSFET), or another suitable type of switch. In the example of IGBTs and FETs, the control terminal is referred to as a gate.

The first terminal of the first switch 516 is connected to the high side 304. The second terminal of the first switch 516 is connected to a node 504. The second terminal of the second switch 520 may be connected to the low side 308. The node 504 is connected to the second terminal of the first switch 516, the first terminal of the second switch 520, and a first phase (e.g., a) of the electric motor 198.

The first leg 512 may include first and second diodes 524 and 528 connected anti-parallel to the switches 516 and 520, respectively. In other words, an anode of the first diode 524 may be connected to the second terminal of the first switch 516, and a cathode of the first diode 524 may be connected to the first terminal of the first switch 516. An anode of the second diode 528 may be connected to the second terminal of the second switch 520, and a cathode of the second diode 528 may be connected to the first terminal of the second switch 520. The diodes 524 and 528 form one phase of a three-phase rectifier for converting power from the electric motor 198 into power for the battery 199. However, the diodes 524 and 528 may be omitted, such as if switches 516, 540, 556, 520, 544, and 560 are MOSFETS (with a built in diode). The diodes 524 and 528 may be included if included with a power module of an IGBT.

The inverter module 316 also includes second and third legs 532 and 536. The second and third legs 532 and 536 may be (circuitry wise) similar or identical to the first leg 512. In other words, the second and third legs 532 and 536 may each include respective switches and diodes like the switches 516 and 520 and the diodes 524 and 528, connected in the same manner as the first leg 512. For example, the second leg 532 includes switches 540 and 544 and anti-parallel diodes 548 and 552. A node 542 is connected to the first terminal of the switch 544, and a second stator winding (e.g., b) of the electric motor 198. The third leg 536 includes switches 556 and 560, and anti-parallel diodes 564 and 568. A node 570 is connected to the first terminal of the switch 560 and a third stator winding (e.g., c) of the electric motor 198. Like the diodes 524 and 528, the diodes 548, 552, 564, and 568 may be omitted.

Control terminals of the switches of the inverter module 316 are connected to switch signals 576 from the motor control module 196. The motor control module 196 generates the switch signals 576 such that the high side switch of a leg is on while the low side switch of that leg is off and vice versa. The motor control module 196 generates the switch signals 576 using pulse width modulation (PWM) control.

The control signals of the gates of the low side switches 520, 544, and 560 may be inverted such that the control signals applied to the low side switches 520, 544, and 560 are opposite in polarity to the control signals applied to the gates of the high side switches 516, 540, and 556.

FIG. 5 is a functional block diagram of an example implementation of the motor control module 196. A switching module 604 controls switching of the switches 516 and 520 using pulse width modulation (PWM) signals. For example, the switching module 604 applies PWM signals to the control terminals of the switches 516, 520, 540, 544, 556, and 560. When a high side switch is on, power flows from the battery 199 to the electric motor 198 to drive the electric motor 198.

The states of the high and low side switches of each phase are complementary (opposite) given the inversion of the signals applied to the gates of the low side switches 520, 544, and 560. For example, the low side switch 520 of the first leg 512 is off when the high side switch 516 of the first leg 512 is on and vice versa. The low side switch 544 of the second leg 532 is off when the high side switch 540 of the second leg 532 is on and vice versa. The low side switch 560 of the third leg 536 is off when the high side switch 556 of the third leg 536 is on and vice versa.

The PWM signals provided to the second and third legs 532 and 536 may be phase shifted from each other and from the PWM signals provided to the switches 516 and 520 of the first leg 512. For example, the PWM signals for each leg may be phase shifted from each other leg by 120° (360°/3 legs=120° shift per leg). In this way, the currents through the stator windings (phases) of the electric motor 198 may be phase shifted by 120° from each other. Different types of PWM schemes for three phase voltage source inverters may be used, such as space vector modulation, sine triangle modulation, third harmonics injection modulation, discontinuous modulation, or another suitable PWM scheme.

A current command module 608 determines a d-axis current command (Id Command) and a q-axis current command (Iq Command) for the electric motor 198 based on the motor torque request 234, a (mechanical) rotor speed 632 of the electric motor 198, and a DC bus voltage 610. The current command module 608 may determine the d- and q-axis current commands using one or more equations and/or lookup tables that relate motor torque requests, rotor speeds, and DC bus voltages to d- and q-axis current commands.

The d-axis current command and the q-axis current command are collectively illustrated by 412 in FIG. 5 . A voltage sensor 611 measures the DC bus voltage 610 between the battery 199 and the inverter module 316 (e.g., between the high and low sides 304 and 308), such as a voltage across a DC bus capacitor. The axis of the magnet field or rotor winding field is called the rotor direct axis or the d-axis. The axis that is 90 degrees after the d-axis is called the quadrature axis or q-axis.

The rotor speed 632 is a (mechanical) rotational speed of the rotor of the electric motor 198. The rotor speed 632 may be measured, for example, using a rotor speed sensor 636. In various implementations, the rotor speed 632 may be determined by a rotor speed module based on one or more other parameters, such change in position of the rotor over time where position is determined based on currents 640 of the electric motor 198. In various implementations, the rotor speed sensor 636 may determine a position of the rotor, and the rotor speed sensor 636 (or a speed module, such as of the motor control module 196) may determine the rotor speed 632 based on a change in the rotor position over time (e.g., using a mathematical derivative of the position with respect to time). Current sensors 642 may measure the phase currents 640, such as in the respective legs of the inverter module 316. In various implementations, one or more of the phase currents 640 may be estimated.

A voltage command module 656 (which may be referred to as a current regulator) determines voltage commands for the electric motor 198 based on the d-axis current command, the q-axis current command, a d-axis current of the electric motor 198, and a q-axis current of the electric motor 198. The d-axis voltage command and the q-axis voltage command are collectively illustrated by 660 in FIG. 5 . In various implementations, the voltage command module 656 may generate the voltage commands 660 using closed-loop control based on or to adjust the d and q-axis currents 644 toward or to the d and q-axis current commands 612, respectively. A frame of reference (FOR) module 648 may transform the phase currents 640 into the d and q-axis currents 644 by applying a Clarke transform and a Park transform.

The switching module 604 determines duty cycles of the PWM signals to apply to the switches of the inverter module 316 to produce voltage for the electric motor 198, respectively, based on the d and q-axis voltage commands. For example, the switching module 604 may determine PWM duty cycle using one or more schemes (e.g., algorithms) which utilize equations or lookup tables that relate voltage commands to PWM duty cycles. Example PWM schemes for three phase voltage source inverters include, but are not limited to, space vector modulation, sine triangle modulation, third harmonic injection modulation, and discontinuous modulation. The switching module 604 switches the switches of the inverter module 316 based on the PWM duty cycles for the phases, respectively, and a target switching frequency 670. The duty cycle of a phase corresponds to the period that the high side switch of the phase is on (closed) during period corresponding to the target switching frequency 670 (period=1/target switching frequency). PWM schemes may have a fixed switching frequency with and a modulated duty cycle.

A target frequency module 674 sets the target switching frequency 670. The target frequency module 674 may set the target switching frequency 670 for each phase. More specifically, the target frequency module 674 sets the target switching for the first phase, the target switching frequency for the second phase, and the target switching frequency for the third phase of the inverter module 316. The target switching frequency for each phase may be the same.

The target frequency module 674 may set the target switching frequency 670 for a phase to a first predetermined switching frequency for a specified length of time during the fundamental electrical cycle or period of the current of the phase when the current ripple of the phase is less than a predetermined value. The first predetermined switching frequency may be, for example, 10 kilohertz (kHz) or another suitable switching frequency. This provides a first predetermined number of ON periods (e.g., 3) of the high side switch per period of the current of the phase. The target frequency module 674 may do this for each phase.

The target frequency module 674 may set the target switching frequency 670 for a phase to a second predetermined switching frequency for a specified length of time within the fundamental electrical cycle or period of the current of the phase when the current ripple of the phase is greater than the predetermined value. The second predetermined switching frequency is greater than the first predetermined switching frequency may be, for example, approximately 15 kHz, approximately 20 kHz, or another suitable switching frequency that is at least 2 kHz greater than the first predetermined switching frequency. This provides a second predetermined number of ON periods (e.g., 6 in the example of the second predetermined switching frequency being twice the first predetermined switching frequency) of the high side switch per period of the current of the phase. The length of time at the first and second predetermined switching frequencies sum to the fundamental electrical period of current. Approximately may mean+/−10% of the stated value. Using the second (higher) predetermined switching frequency may increase a loss (e.g., switching) of the inverter module 316. However, the use of the second predetermined switching frequency decreases AC current ripple, decreases a loss of the electric motor 198, decreases a total loss of the system, decreases DC bus capacitor root mean square (RMS) current and loss, and decreases AC current total harmonic distortion (THD). The use of the second predetermined switching frequency also decreases noise, vibration, and harshness (NVH) of the motor, and decreases potential resonances, and makes torque of the motor smoother.

The target frequency module 674 may set the period (duration) and timing of the period to set the target switching frequency 670 to the second predetermined switching frequency based on a torque 669 of the electric motor 198 and the speed 632 of the electric motor 198. The target frequency module may set the period and the timing (e.g., start) for use of the second predetermined switching frequency the period using one or more equations or lookup tables that relate motor torques and speeds to periods and timings for use of the second predetermined switching frequency.

A torque sensor 668 may measure the present torque 669 of the electric motor 198. In various implementations, the present torque 669 may be estimated by a torque estimation module based on one or more parameters.

Alternatively to determine the period and timing for use of the second predetermined switching frequency based on the present torque 669 and the speed 632, the target frequency module 674 may set the period and timing of the period to set the target switching frequency 670 to the second predetermined switching frequency based on the three phase currents. For example, the target frequency module 674 may set the period and timing of the period for use of the second predetermined switching frequency for the phases based on the ripple current content of the first, second, and third phases (Ia, Ib, Ic).

Alternatively to determine the period and timing for use of the second predetermined switching frequency based on the present torque 669 and the speed 632, the target frequency module 674 may set the period and timing of the period to set the target switching frequency 670 to the second predetermined switching frequency based on at least one of the d-axis current and the q-axis current 644. For example, the target frequency module 674 may set the period and timing of the period for use of the second predetermined switching frequency for the first, second, and third phases using one or more equations and/or lookup tables that relate d-axis and/or q-axis current ripples to periods and timings for the phases.

Alternatively to determining the period and timing for use of the second predetermined switching frequency based on the present torque 669 and the speed 632, the target frequency module 674 may set the period and timing of the period of a phase to set the target switching frequency 670 to the second predetermined switching frequency based on the magnitude of a stator current space vector (Iss). The target frequency module 674 may determine the stator current space vector based on the d-axis current and the q-axis current 644. For example, the target frequency module 674 may set the stator current based on or equal to the square root of the sum of (a) the d-axis current squared and (b) the q-axis current squared. For example, the target frequency module 674 may set the period and timing of the period for use of the second predetermined switching frequency for the phases using one or more equations and/or lookup tables that relate stator current ripples to periods and timings for the phases.

The switching module 604 switches the switches of the phases of the inverter module 316 based on the PWM duty cycles and the target switching frequencies of the phases, respectively.

FIG. 6 is an example graph of gate signals during a portion of a fundamental electrical period or cycle applied to the first phase (phase A) 704 of the electric motor 198, gate signals applied to the second phase (phase B) 708 of the electric motor 198, and gate signals applied to the third phase (phase C) 712 of the electric motor 198. A gate signal of positive 1 may mean that the high side switch of that phase (e.g., 516 of the first phase 512) is closed and the low side switch of that phase (e.g., 520 of the first phase 512) is open. A gate signal of negative 1 may mean that the high side switch of that phase (e.g., 516 of the first phase 512) is open and the low side switch of that phase (e.g., 520 of the first phase 512) is closed.

The left column 716 of graphs illustrates the gate signals of the phases, respectively, without changing the target switching frequency. In other words, only the first predetermined switching frequency is used for the graphs of the left column 716 of FIG. 6 .

The right column 720 includes graph of gate signals applied to the first phase (phase A) 724 of the electric motor 198, gate signals applied to the second phase (phase B) 728 of the electric motor 198, and gate signals applied to the third phase (phase C) 732 of the electric motor 198. The right column 720 of graphs illustrates the gate signals of the phases, with selectively using the first predetermined switching frequency and the second predetermined switching frequency. Graph 736 illustrates whether the first predetermined switching frequency or the second predetermined switching frequency is used. More specifically, when the signal of graph 736 is at 2, the second predetermined switching frequency is used, and when the signal of graph 736 is at 1, the first predetermined switching frequency is used. As illustrated by graphs 724, 728, and 732, switching is more frequent when the (higher) second predetermined switching frequency is used. For example, 3 PWM cycles per phase period may be used with the first predetermined switching frequency, and 6 PWM cycles per phase period may be used with the second predetermined switching frequency.

The current ripple pattern repeats at six times the fundamental electrical frequency of the sinusoidal phase currents. Since the aim is to reduce the current ripple, the control and change implementation of the predetermined switching frequency 1 and predetermined switching frequency 2 is done six time during the period of AC currents. The start time and the length of time of each switching frequency are determined using the aforementioned ripple criteria which can be done in real time or precalibrated (e.g., using a lookup table).

FIG. 7 is a flowchart depicting an example method of selectively varying (e.g., doubling) the switching frequency of the inverter module 316 and controlling switching of the inverter module 316. Control begins with 804 where motor torque request 234 is determined as discussed above.

At 808, the current command module 608 determines the d-axis current command and the q-axis current command as described above. At 812, the voltage command module 656 determines the d-axis voltage command and the q-axis voltage command based on the d-axis current command, the d-axis current, q-axis current command, and the q-axis current.

At 816, the switching module 816 determines the target duty cycles for the phases, respectively, based on the d-axis voltage command and the q-axis voltage command. At 820, the target frequency module 674 determines the target switching frequency 670 based on at least one of: (1) the torque 669 and the speed 632 of the motor; (2) the d-axis current; (3) the q-axis current; (4) the stator current; and (5) at least one of the phase currents. The target frequency module 674 sets the target switching frequency 670 to either the first predetermined switching frequency (e.g., 10 kHz) or the second predetermined switching frequency (e.g., 20 kHz).

At 824, the switching module 604 switches the switches of the phases at the target duty cycles, respectively, at the target switching frequency. While the example of FIG. 7 is shown as ending, control may return to 804 for a next control loop. FIG. 8 includes an example graph of phase currents 804, d-axis current 808, q-axis current 812, and ISS 816 and a ripple tracking pulse 820 over time.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.

In this application, including the definitions below, the term “module” or the term “controller” may be replaced with the term “circuit.” The term “module” may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, data structures, and/or objects. The term shared processor circuit encompasses a single processor circuit that executes some or all code from multiple modules. The term group processor circuit encompasses a processor circuit that, in combination with additional processor circuits, executes some or all code from one or more modules. References to multiple processor circuits encompass multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term shared memory circuit encompasses a single memory circuit that stores some or all code from multiple modules. The term group memory circuit encompasses a memory circuit that, in combination with additional memories, stores some or all code from one or more modules.

The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that are stored on at least one non-transitory, tangible computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language), XML (extensible markup language), or JSON (JavaScript Object Notation) (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5th revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®. 

What is claimed is:
 1. A motor control system comprising: a voltage command module configured to determine a target d-axis voltage for an electric motor and a target q-axis voltage for the electric motor; a target frequency module configured to: selectively set a target switching frequency to a first predetermined switching frequency; and selectively set the target switching frequency to a second predetermined switching frequency that is at least 2 kilohertz (kHz) greater than the first predetermined switching frequency; and a switching module configured to: based on the target d-axis voltage and the target q-axis voltage, determine target pulse width modulation (PWM) duty cycles for phases, respectively, of the electric motor; and switch switches of legs of an inverter module connected to the phases of the electric motor at the target PWM duty cycles, respectively, and the target switching frequency.
 2. The motor control system of claim 1 wherein the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a torque of the electric motor and a speed of the electric motor.
 3. The motor control system of claim 2 wherein the target frequency module is configured to: based on the torque and the speed, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency within the fundamental electrical period of sinusoidal phase current; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.
 4. The motor control system of claim 1 wherein the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a d-axis current of the electric motor.
 5. The motor control system of claim 4 wherein the target frequency module is configured to: based on the d-axis current of the electric motor, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.
 6. The motor control system of claim 1 wherein the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a q-axis current of the electric motor.
 7. The motor control system of claim 6 wherein the target frequency module is configured to: based on the q-axis current of the electric motor, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.
 8. The motor control system of claim 1 wherein the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on at least one current of at least one of the phases of the electric motor.
 9. The motor control system of claim 8 wherein the target frequency module is configured to: based on the at least one current of the at least one of the phases, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.
 10. The motor control system of claim 1 wherein the target frequency module is configured to determine whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a stator current that is equal to a square root of a sum of (a) a d-axis current of the electric motor squared and (b) a q-axis current of the electric motor squared.
 11. The motor control system of claim 10 wherein the target frequency module is configured to: based on the stator current, set a starting time and a period for setting the target switching frequency to the second predetermined switching frequency; and set the target switching frequency to the second predetermined switching frequency at the starting time for the period.
 12. The motor control system of claim 1 wherein the first predetermined switching frequency is 10 kHz.
 13. The motor control system of claim 12 wherein the second predetermined switching frequency is approximately 15 kHz.
 14. The motor control system of claim 12 wherein the second predetermined switching frequency is approximately 20 kHz.
 15. The motor control system of claim 1 wherein the voltage command module is configured to determine the target d-axis voltage for the electric motor and the target q-axis voltage for the electric motor based on minimizing: a first error between a d-axis current of the electric motor and a target d-axis current of the electric motor; and a second error between a q-axis current of the electric motor and a target q-axis current of the electric motor.
 16. The motor control system of claim 15 further comprising a current command module configured to set the target d-axis current and the target q-axis current based on a torque request for the electric motor.
 17. The motor control system of claim 1 wherein the target frequency module is configured to selectively set the target switching frequency to the second predetermined switching frequency for 6 different periods during the period of a fundamental electrical period of sinusoidal phase current.
 18. A motor control method comprising: determining a target d-axis voltage for an electric motor and a target q-axis voltage for the electric motor; selectively setting a target switching frequency to a first predetermined switching frequency; selectively setting the target switching frequency to a second predetermined switching frequency that is at least 2 kilohertz (kHz) greater than the first predetermined switching frequency; based on the target d-axis voltage and the target q-axis voltage, determining target pulse width modulation (PWM) duty cycles for phases, respectively, of the electric motor; and switching switches of legs of an inverter module connected to the phases of the electric motor at the target PWM duty cycles, respectively, and the target switching frequency.
 19. The motor control method of claim 18 further comprising determining whether to set the target switching frequency to the first predetermined switching frequency or the second predetermined switching frequency based on a torque of the electric motor and a speed of the electric motor.
 20. The motor control method of claim 19 further comprising: based on the torque and the speed, setting a starting time and a period for setting the target switching frequency to the second predetermined switching frequency within the fundamental electrical period of sinusoidal phase current; and setting the target switching frequency to the second predetermined switching frequency at the starting time for the period. 